Mechanically tuned loop antenna



April 10,1945. T S Q 2,373,206

MECHANIGALLY TUNED LOOP ANTENNA Filed April 30,}942

as Fifi-.1.

16 Z2 Z1 Zhioentor u$ Harry E. Thomas (Ittorneg Patented Apr. 10, 1945UNITED STATES PATENT OFFICE MECHANICALLY TUNED LOOP ANTENNA Harry E.Thomas, Haddonfield, N. J assignor to Radio Corporation of America, acorporation of Delaware Application April'30, 1942, Serial No. 441,112

1 Claim. (Cl. 250-33) This invention relates generally to variableinductive devices and particularly to mechanically tuned inductors orloop antennas comprising a plurality of loops and means for varying themutual inductance between three or more of the loops.

From the standpoint of economical receiver construction, it is quitedesirable to tune the antenna circuit and the input circuit to the firstradio frequency tube by means of a variable inductance in conjunctionwith a fixed capacitor. Heretofore, considerable difiiculty has beenexperienced in designing a suitable variable inductance having aninductance ratio of the order of nine to one which is necessary fortuning This invention contemplates the use of a tuned inductor or loopantenna having satisfactoryeificiency throughout the desired frequencyband, and providing for a ratio of minimum to maximum inductances of theorder of ten to one.-.

The invention is adapted to simple and inexpensive mechanical design,and may provide tuning The;

tuned loop of the invention includes, "by way of example, four loopsserially connected, mounted upon a. collapsible, hinged frame in such amanner that maximum inductance is provided when the frame is in oneposition and a gradual reduction of inductance is provided as the shapeof the frame is changed.

Among the objects of the invention are to provide an improved method ofand means for combining a plurality of inductors, adjustable withrespect to each other, for varying the total inductance of the circuit.Another object of the invention is to provide an improved method of andmeans for combining a. plurality of inductors mounted upon a suitablecollapsible hinged frame. Still another object is to provide an improvedmethod of and means for adjusting the relative positions of a pluralityof serially con-- nected inductors hinged with respect to each other. Afurther object is to provide an improved variable inductance comprisinga plurality of interconnected coils, hinged with respect to each other,and means for varying the relative position of the coils to change themutual inductance thereof. Another object is to provide a variablefilter circuit comprising a plurality of tuned circuits havingsubstantially constant inductive coupling, the tuning of said tunedcircuits being a function of the mutual inductance between the inductivecircuit components.

The invention will be described by reference to the drawing of whichFigure 1 is a perspective view of one embodiment of the invention;Figure 2 is a schematic diagram of the same emlbodiment of theinvention; Figure 3 is a plan view of a. modification of the invention;Figure 4 is an elevational view of the operating device comprising acomponent of Fig. 3; Figure 5 is a schematic diagram of a secondembodiment of the invention; and Figure 6 is an equivalent circuitdia-,- gram of the embodiment of Fig. 5. Similar refer-- ence numeralsare applied to similar elements throughout the drawing.

Referring to Fig. 1, four loops, I, 2, 3, and 4,- wound in the samedirection, are mounted upon-- four supports II, I2, I3, and I4,respectively, which are hinged to each other to form a hollow bodyhaving substantially square cross section. I

It is apparent that if the loops are constructed to he self-supporting,for example, collodion supported windings, the supports I I, I2, I3 andI4 may be omitted and the windings directly hinged to each other bysuitable cloth or other type- Any suitable means of securing the suphinges. port I3 to a suitable base, and varying the angular relation of.the supports I I, I2, and I4 thereto, may be provided.

Fig. 2 is a schematic diagram showing the direction of the currents atany instant through the four serially connected coils I, 2, 3 and 4'.The connections between the coil terminals are indicated by the pigtailconnections 3|, 32, and 33. When the coils 2 and 4 are substantiallynormal to the coils I and 3, the mutual inductance between the coils 2and 4 is additive, and the mutual inductance between the coils I and 3is also additive, while the mutual coupling be tween the coils normal toeach other is at a low value. As the coils 2 and 4 are rotatedcounterclockwise with respect to the coil 3, for example, to theposition 5, the mutual inductance between the coils I and 3 and themutual inductance between the coils 2 and 4 is decreased. The currentsin the coils 2 and 3 and the currents in the coils I and 3 are in phaseopposition, to a degree depending upon the angle of rotation. If thecoils 2 and 4 are rotated clockwise with respect to the coil 3, themutual inductance between the coils i and 3 and the mutual inductancebetween the coils 2 and 4 is gradually reduced, but the mutualinductance between the coils l and 4 and the mutual inductance betweenthe coils 2 and 3 is increased to a relatively high value as the angleof rotation is increased, due to the extremely close coupling betweenthese coils at the extreme clockwise adjustment. A fixed tuningcondenser 25 is connected across the output terminals 26 to tune theloop circuit to the desired minimum frequency at the maximum inductiveadjustment.

Fig. 3 is similar to the device described by reference to Fig. 1 withthe addition of a typical actuating device for adjusting the relativeangular relation of the four loops. The actuating device includes abearing 2| mounted on a suit able support 20. A shaft 22, journalled inthe bearing 2 l, carries a crank arm 23 which includes g two pins 24which contact opposite faces of one of the vertical coil supports Hi. Ifthe axis of the shaft '22 coincides with the hinge between the supportsl3 and 4, a reasonably close fit maybe provided between the support Mand the pins 24 thereby eliminating substantially all back-lash. Anysuitable well known means for providing non-linear angular adjustmentmay be substituted to facilitate tuning. Fig. 4 is a side view of thetuning device and shows the shaft 22, crank 23, pin 2 1, and coilsupport M.

It will be apparent that the constructional details may be variedconsiderably without deviating from the principles of the invention andthat various modifications of the invention may be made insofar as theyare necessary to the particular requirements of radio circuits otherthan antenna circuits. For example, the device may be made withrelatively small compact coils suitable for use as a tuning inductance.Also suitable means may be provided for coupling circuits to thevariable inductance provided by the invention, such as the coil 6 infixed inductive relation to the coil 3. (See Fig. 1.) When the inventionis adapted to use as a tuned loop antenna, thepickup throughout theuseful frequency range has been found to be relatively uniform and thevariation of inductance to resistance has been found to followwell-known practice. Flat wound coils are preferable when used as a loopantenna, since they provide higher mutual inductance and better signalpickup, while also being highly adaptable to simple and economicalconstruction.

Fig. 5 schematically illustrates one method of 5 parallel with a fixedtuning capacitor 31.

combining six windings, arranged hexagonally to provide a bandpasstuning device, comprising a tuned primary circuit including a first coil32 connected in series with a second coil 33, both in A link circuit,including a serially connected stationary coil 3! and a movabl coil 34,provides substantially constant coupling between the primary circuit anda secondary tuned circuit comprising 10 the serially connected coils 35and 36, both in parallel with a second tuning capacitor 38. Inputcurrents are applied to the terminals 39 and output currents are derivedfrom the terminals 40. Th windings 32 and 33 are connected to provideaiding fields whereby an increas in mutual inductance results as thewinding 32 is rotated counterclockwise with respect to the stationarycoil 3|. The windings. 35 and 36 are connected to provide opposingfields whereby a similar increas in mutual inductance may be kept at alow value. It should be understood that any other number andarrangement,

including polarity, of coils may be used to provide a desired filtercircuit without departing from the scop of the invention defined by theappended claim.

I claim as my invention: A variable inductive device including at leastthree interconnected windings, means including separate insulatingsubstantially fiat members 40 supporting each of said windings, hingemeans for varying simultaneously the relative position ,and angularrelation of said supporting members and hence said windings to vary themutual inductance between at least two of said windings and for varyingsimultaneously in the opposite sense the mutual inductance between saidtwo windings and the balance of said windings and eccentric meansrotatable on the axis of one of said hinge means having an eccentricportion thereof in engagement with one of said insulat-" ing members forvarying the angular relation and relative positions of said windings.

I HARRY E. THOMAS.

